Device and method for the thermal fogging of a liquid

ABSTRACT

Device for the thermal fogging of a liquid, said device comprising:
         an unit ( 3 ) for producing a stream of pressurised hot gas;   an ejection pipe ( 5 );   a first source ( 7 ) of liquid;   means ( 9 ) for injecting a measured flow of liquid into the ejection pipe ( 5 ) from the first source ( 7 ) of liquid;
 
characterised in that it comprises
   a sensor ( 11 ) for detecting a total or partial interruption of the measured flow of liquid injected into the ejection pipe ( 5 ) from the first source ( 7 ) of liquid;   a second source ( 13 ) of liquid;   means ( 15 ) for injecting an emergency flow of liquid into the ejection pipe ( 5 ) from the second source ( 13 ) of liquid when the sensor ( 11 ) detects a total or partial interruption of the measured flow of liquid injected into the ejection pipe ( 5 ) from the first source ( 7 ) of liquid.

BACKGROUND OF THE INVENTION

The invention relates in general to the thermal fogging of liquids.

SUMMARY OF THE INVENTION

More precisely, the invention relates, in a first aspect, to a devicefor the thermal fogging of a liquid, of the type comprising:

-   -   an unit for the production of a pressurised hot gas stream,        having a hot gas outlet;    -   an ejection pipe, having a hot gas inlet connected to the hot        gas outlet of the production unit, and an ejection outlet for a        mist of liquid;    -   a first source of liquid;    -   means for injecting a measured flow of liquid into the ejection        pipe from the first source of liquid.

Such a device is known from FR 2 566 681, which discloses that theliquid is injected into the ejection pipe by a pump extracting saidliquid in a tank. The stream of gas consists of air, heated by anelectrical resistor.

Fires may occur on this type of thermal fogging machine, particularlywhen the pump has lost prime.

In this context, the invention aims to propose a thermal fogging devicein which the fire risk is reduced.

The invention therefore relates to a thermal fogging device of theabove-mentioned type, characterised in that it comprises:

-   -   a sensor for detecting the total or partial interruption of the        measured flow of liquid injected into the ejection pipe from the        first source of liquid;    -   a second source of liquid;    -   means for providing at the liquid inlet an emergency flow of        liquid from the second source of liquid when the sensor detects        a total or partial interruption of the measured flow of liquid        injected into the ejection pipe from the first source of liquid.

The device may also have one or more of the characteristics below,considered individually or in all the technically possible combinations:

-   -   the means for injecting a measured flow of liquid into the        ejection pipe from the first source of liquid comprise a liquid        measuring device, having a liquid suction inlet connected to the        first source of liquid and a liquid delivery outlet connected to        a liquid inlet of the ejection pipe, the means for injecting an        emergency flow of liquid into the ejection pipe from the second        source of liquid comprising a valve component suitable for        selectively connecting the liquid suction inlet of the measuring        device to the second source of liquid;    -   the sensor is a temperature sensor suitable for measuring the        current temperature of the gas in the ejection pipe downstream        of the liquid inlet;    -   the device comprises a computer suitable for taking the current        temperature of the gas measured by the sensor, comparing this        current temperature with a predetermined maximum value, and        actuating the valve component to connect the liquid suction        inlet of the measuring device to the second source of liquid        when the current temperature is higher than said predetermined        maximum value;    -   the valve component comprises a three-way valve comprising a        first liquid inlet connected to the first source of liquid, a        second liquid inlet connected to the second source of liquid and        an outlet connected to the liquid suction inlet of the measuring        device;    -   the first source of liquid is a source of a liquid containing a        chemical treatment agent, the second source of liquid being a        source of a liquid that does not contain said chemical treatment        agent;    -   the second source of liquid is a source of water;    -   the unit for producing a stream of pressurised hot gas comprises        a fan, provided with a gas suction inlet and a pressurised gas        delivery outlet, and a device for heating the pressurised gas,        having a cold gas inlet connected to the delivery outlet of the        fan, and an outlet forming the hot gas outlet; and    -   the second source of liquid is a substantially airtight tank,        means for injecting an emergency flow of liquid into the        ejection pipe from the second source of liquid comprising a        pressurising pipe connecting the delivery outlet of the fan to a        crown of the second source of liquid, and an injection pipe        connecting the second source of liquid to a liquid inlet of the        ejection pipe.

According to a second aspect, the invention relates to a method for thethermal fogging of a liquid, this method comprising the following steps:

-   -   creating a current of pressurised hot gas;    -   injecting a flow of liquid into the pressurised hot gas from a        first source of liquid;        characterised by the following steps:    -   detecting a total or partial interruption of the flow of liquid        coming from the first source of liquid;    -   injecting a flow of liquid into the pressurised hot gas from a        second source of liquid when a total or partial interruption of        the flow of liquid coming from the first source of liquid is        detected.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other characteristics and advantages of the invention will emerge fromthe description given below as a non-limiting indication, with referenceto the accompanying drawings, in which,

FIG. 1 is a simplified diagrammatic illustration of a thermal foggingdevice according to a first embodiment of the invention,

FIG. 2 is a similar illustration to that of FIG. 1, for a secondembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The device illustrated in FIG. 1 is a thermal fogging device forproducing a stream of gas comprising a mist of liquid. The mist ofliquid comprises very fine droplets, at least 90% of the dropletspreferably having a diameter less than or equal to 3 microns.

Such a device is typically provided for the treatment of fruit andvegetables stored in enclosed areas, particularly greenhouses or storageareas.

The liquid forming the mist is typically an aqueous solution comprisinga chemical agent suitable for the treatment of fruit and vegetables.This chemical agent has for example a protective action intended toprolong the conservation of fruit and vegetables. It may have anantioxidant effect, an anti-germinative effect and/or a fungicidaleffect. Such compositions are described in FR 2 728 142, FR 2 786 664and FR 2 791 910.

The thermal fogging device 1 comprises:

-   -   an unit 3 for producing a stream of pressurised hot gas;    -   an ejection pipe 5;    -   a first source 7 of a liquid containing a chemical treatment        agent;    -   means 9 for supplying a measured flow of liquid to the ejection        pipe from the first source 7;    -   a sensor 11 for detecting a total or partial interruption of the        measured flow of liquid coming from the first source of liquid;    -   a second source 13 of liquid;    -   means 15 for supplying an emergency flow of liquid to the        ejection pipe from the second source of liquid when the sensor        11 detects a total or partial interruption of the measured flow        of liquid coming from the first source of liquid 7.

The production unit 3 comprises a fan 17 and a heating device 19. Thefan 17 has an inlet for extracting air from the atmosphere (notillustrated) and an outlet 21 for delivering pressurised air.

The heating device 19 comprises an envelope 23, a heating resistor 25and an electrical supply 27 connected electrically to the electricalresistor 25. The electrical resistor 25 is situated inside the envelope23. The envelope 23 has a cold gas inlet connected to the deliveryoutlet 21 of the fan, and a tapering portion 29 defining an outlet 31for pressurised hot gas.

The ejection pipe 5 is a rectilinear cylindrical pipe. It is open atboth ends. One of the ends defines a hot gas inlet connected to theoutlet 31 of the heating device. The opposite end defines an ejectionoutlet for a hot gas stream loaded with a mist of liquid. This outlethas the reference numeral 33. The ejection pipe also comprises a liquidinlet 35 situated near the hot gas inlet.

The first source 7 of liquid is typically a tank filled with treatmentliquid. This liquid is typically water containing a chemical treatmentagent.

The means 9 for supplying a measured flow of liquid to the ejection pipecomprise a volumetric pump 37, a suction pipe 39, a delivery pipe 41, athree-way valve 43 and a connection pipe 45. The suction pipe 39connects the suction inlet of the pump 37 to the tank 7. The deliverypipe 41 connects a delivery outlet of the measuring pump 37 to an inletof the three-way valve 43. The connection pipe 45 connects a firstoutlet of the three-way valve 43 to the liquid inlet 35 of the ejectionpipe. Furthermore, a return pipe 47 connects a second outlet of thethree-way valve 43 to the tank 7.

The temperature sensor 11 is placed in the ejection pipe 5, downstreamof the liquid inlet 35. It is placed preferably near the ejection outlet33. It provides information to a computer 49.

The second source of liquid 13 is for example a tank filled with water.This water does not contain a chemical treatment agent.

The means 15 for supplying an emergency flow to the liquid inlet fromthe second source of liquid comprise a three-way valve 51, inserted inthe suction pipe 39, and a suction duct 53.

A first portion 55 of the suction pipe 39 connects the tank 7 to aninlet of the three-way valve 51. Another portion 57 of the suction pipeconnects an outlet of the three-way valve 51 to the suction area of themeasuring pump 37. The suction duct 53 connects the second source 13 ofliquid to a second inlet of the three-way valve 51.

The shaft 59 of the fan 17 is driven by an electric motor that has notbeen illustrated. This shaft 59 in turn drives the volumetric pump 37,for example by means of a belt 60 or directly.

The computer 49 is connected to the temperature sensor 11, to theelectric generator 27, to the motor of the fan 17 and to the three-wayvalves 43 and 51. The computer 49 is suitable for controlling each ofthese elements.

The fan 17 has a pressure difference between delivery and suction ofbetween 0.20 10⁵ Pa and 0.30 10⁵ Pa, preferably between 0.22 10⁵ Pa and0.30 10⁵ Pa. The output of the fan varies between 30 and 80 Nm³/h,preferably between 55 and 70 Nm³/h. The linear speed of the hot air atthe inlet of the pipe 5 is therefore between 160 and 400 m/s, preferablybetween 200 and 280 m/s. The electrical resistor 25 is dimensioned to becapable of heating the air to a temperature of between 550 and 750° C.at the inlet of the pipe 5. Preferably, the electrical resistor 25 isdimensioned to heat the air to a temperature of between 600 and 700° C.,and even more preferably between 600 and 650° C. The electrical power ofthe resistor is between 5 and 20 kW, and preferably has a value ofbetween 7.5 and 10 kW.

At the ejection outlet of the pipe 5, the mist of liquid comprisesdroplets having a temperature of between 200 and 280° C., driven at alinear speed of between 110 and 140 m/s.

To satisfy these conditions, the following criteria, in addition to theparameters described above, may be suitably adapted:

-   -   the length of the pipe 5;    -   the diameter of the pipe 5;    -   the output and temperature of the liquid injected at the inlet        35 of the pipe 5.

The diameter of the pipe 5 is generally between 12 and 25 mm, preferablybetween 15 and 20 mm, and even more preferably between 16 and 18 mm.

The length of the pipe 5 is generally between 300 and 1500 mm. Theinjection output of liquid from the first source of liquid 7 at theinlet 35 of the pipe 5 is generally between 5 and 30 litres per hour,preferably between 10 and 25 litres per hour, and even more preferablybetween 13 and 20 litres per hour. The temperature of the liquidinjected into the pipe 5 is generally between 10 and 30° C., preferablybetween 15 and 25° C., and even more preferably between 20 and 25° C.

In an embodiment, the fan 17 provides a difference in pressure betweensuction and delivery of 25,000 Pascal, and an output of 60 Nm³/h. Thepipe 5 has a diameter of 18 mm and a length of 800 mm. The electricalresistor 25 has an electrical power of 10 kW. The temperature of the hotair at the inlet of the pipe 5 is about 600° C. The linear speed of thehot air at the inlet of the pipe 5 is about 220 m/s. The liquid isinjected at the inlet 35 of the pipe 5 at an output of 15 litres perhour, and at a temperature of 20 to 25° C. At the ejection outlet 33 ofthe pipe a mist of droplets is obtained which have an average diameterof 0.4 microns. The linear speed of the droplets at the outlet of thepipe 5 is 125 m/s and the temperature of the droplets is about 240° C.

The operation of the above thermal fogging device will now be described.

At start up, the computer 49 actuates the three-way valve 43 to isolatethe connection pipe 45 and connect the delivery pipe 41 and the returnpipe 47. In addition, the computer 49 actuates the three-way valve 51 toisolate the suction duct 53 and connect the two portions 55 and 57 ofthe suction pipe 39. The computer 49 activates the start up of the fan17 and the electrical supply of the resistor 25. The fan 17 extractsatmospheric air and delivers it through the heating device 19 to thepipe 5. The measuring pump 37 is driven by the shaft 59 of the fan. Itextracts the treatment solution in the tank 7 by means of the suctionpipe 39 and delivers it to the tank 7 via the pipes 41 and 47.

When the temperature measured by the sensor 11 exceeds a minimumpredetermined value, for example 350° C., the computer 49 actuates thethree-way valve 43 to isolate the return pipe 47 and connect thedelivery pipe 41 with the connection pipe 45. The treatment liquidextracted by the volumetric pump 37 in the tank 7 is delivered by thepump to the inlet 35. This liquid is then injected into the stream ofhot gas at over 600° C. coming from the heating device. The liquid isdispersed in the stream of hot gas and split into very fine droplets.Some of the liquid may be vaporised. Under the effect of the injectionof liquid, the stream of gas is cooled, and its temperature falls fromabout 625° C. to about 240° C.

The computer 49 constantly monitors the temperature of the gas streamloaded with the mist of liquid downstream of the inlet 35, by means ofthe sensor 11.

If the flow of liquid coming from the first source 7 of liquid istotally or partially interrupted, the temperature measured by the sensor11 increases. This interruption may result for example from the factthat the tank 7 is empty, all the liquid having already been injected inthe pipe 5. This interruption may also result from the fact that theportion 55 of the suction pipe is totally or partially blocked. Becauseless liquid is injected, or not injected at all into the pipe 5, thestream of gas is no longer cooled in the same way, and the temperatureof the stream of gas increases at the sensor 11.

When the computer 49 detects that the temperature measured by the sensor11 exceeds a maximum predetermined value, for example 400° C., itactuates the three-way valve 51 to isolate the portion 55 and connectthe suction duct 53 with the portion 57.

The volumetric pump therefore extracts the water contained in the secondsource of liquid, namely the tank 13.

The pump 37 delivers the water by means of the pipes 41 and 45 to theinlet 35 of the ejection pipe. The output of liquid from the secondsource of liquid 13 is the same as that from the first source of liquid7: The renewed injection of liquid inside the pipe 5 causes a cooling ofthe hot gases, which are once more reduced to a temperature of about240° C.

A second embodiment of the invention will now be described, withreference to FIG. 2. Only the points on which the second embodimentdiffers from the first will be detailed below.

Elements that are identical, or perform the same function, will bedesignated by the same reference numerals in both embodiments.

The means 15 of supplying an emergency flow of liquid to the ejectionpipe from the second source 13 of liquid comprise in the secondembodiment a pressurising pipe 61 of the tank 13, a solenoid valve 62inserted in the pipe 61, and an injection pipe 63 connecting the tank 13to a second liquid inlet 65 of the ejection pipe 5.

The pipe 61 connects the delivery area of the fan 17 to the crown of thetank 13. An upstream end of the pipe 61 is therefore connected to thedelivery outlet 21 of the fan. The downstream end of the pipe 61 opensinto the crown of the tank 13.

The solenoid valve 62 is an on-off valve, controlled by the computer 49.It can allow or prevent the circulation of air from the delivery area ofthe fan to the crown of the tank 13.

In this second embodiment, the tank 13 is airtight. It comprises forexample a vat 67 open at the top, and a cover 69 for closing the vat 67.Sealing means are arranged between the cover and the vat, to prevent airleaks when the tank 13 is maintained at a pressure at least equal to thedelivery pressure of the fan 17. The pipe 61 is attached to the cover69. For example, the end of the pipe 61 is welded to the cover 69.

An upstream end of the injection pipe 63 passes through the cover 69 anddescends into the water contained in the tank 13. A seal is producedbetween the pipe 63 and the cover 69. This seal is produced for exampleby welding the pipe 63 on the cover 69. Alternatively, a sealing gasketmay be inserted between the pipe 63 and the cover 69.

The tank 13 is partially filled with water, the upper portion 71 of thetank, also known as the crown, being normally filled with air.

The second liquid inlet 65 of the ejection pipe is situated near the hotgas inlet, in other words near the first inlet 35.

The operation of the thermal fogging device according to the secondembodiment of the invention will now be described.

Start up is similar to that of the device according to the firstembodiment of the invention, except that the computer 49 actuates thesolenoid valve 62 to close the pressuring pipe 61. Said valve 62 is keptclosed during normal operation of the thermal fogging device, in otherwords as long as the computer 49 does not detect that the temperaturemeasured by the sensor 11 has exceeded the maximum predetermined value.

However, when the computer 49 detects that the temperature measured bythe sensor 11 exceeds said maximum value, it actuates the opening of thesolenoid valve 62.

The crown 71 of the tank 13 is then connected with the delivery area ofthe fan 17. Thus, the contained liquid is put under pressure, since thepressure that then prevails in the crown 71 corresponds to the deliverypressure of the fan 17.

The water contained in the tank 13 is delivered by pressure to theinjection pipe 63. This water is injected into the pipe 5 via the secondliquid inlet 65.

It should be noted that the air pressure inside the ejection pipe 5 islower than the air pressure at the delivery outlet 21 of the fan,because of the pressure loss that occurs in the heating device. Thus,the pressure in the crown of the tank 13 is higher than the pressureinside the ejection pipe 5. The section of the injection pipe 63 isdimensioned such that this difference in pressure allows sufficientoutput of liquid to cool the stream of hot gas entering the pipe 5.

The thermal fogging device described above has many advantages.

Because it comprises a sensor to detect a total or partial interruptionof the measured flow of liquid injected into the ejection pipe from thefirst source of liquid, a second source of liquid, and means forinjecting an emergency flow of liquid into the ejection pipe from thesecond source of liquid when the sensor detects a total or partialinterruption of the measured flow of liquid injected into the ejectionpipe from the first source of liquid, the fire risks are significantlyreduced.

In fact, the second source of liquid takes over from the first source ofliquid once there is an interruption of the flow from the first source.Thus, the stream of hot gas passing through the pipe 5 does not remainat a high temperature for long.

It has in fact been seen that the pipe 5 may have solid deposits ofchemical treatment agents. These residues have a spontaneous ignitionpoint of about 450° C. If, because of the interruption of the supply ofliquid, the stream of hot gas entering the ejection pipe is no longercooled for a significant period, these residues may catch fire. Becauseof the invention, the second source of liquid quickly takes over fromthe first source of liquid, so that the gas stream never reaches thetemperature of 450° C., or reaches it only fleetingly and is immediatelyreduced to a temperature of less than 450° C. once the second source ofliquid takes over from the first.

It is particularly advantageous to use a temperature sensor to detectthe total or partial interruption of the flow of liquid from the firstsource, given that the intention is to prevent the rise in temperatureof the gas and the spontaneous ignition of the residues.

The means for supplying an emergency flow of liquid to the ejection pipefrom the second source may be produced particularly economically in theform of a three-way valve inserted in the suction pipe of the volumetricpump, an inlet of which is connected by a suction duct to the secondsource of liquid. It is therefore not necessary to make provision for asecond pump to back up the first.

It is particularly advantageous to provide for the second source ofliquid to be a sealed tank and for the means of supplying an emergencyflow of liquid to an ejection pipe from the second source to comprise apressurising pipe connecting the delivery outlet of the fan to the crownof the sealed tank and an injection pipe connecting the sealed tank tothe ejection pipe. Thus, when the interruption of the flow of liquidinjected from the first source is due to a failure of the measuringpump, the second source of liquid may take over despite the pumpfailure. Similarly, if the interruption results from the loss of primeof the pump, the switch to the second source of liquid is also easier asthere is no need to reprime the pump.

The thermal fogging device may have many variants.

The unit for producing a stream of pressurised hot gas does notnecessarily consist of a fan coupled to an electrical resistor. The fanmay be replaced by a compressor or any other type of device that cansupply pressurised gas. The heating device may not be an electricalresistor, but a gas heater, or a heater of any suitable type.

The sensor allowing an interruption of the flow of liquid coming fromthe first source to be detected may not be a temperature sensor. Thisdevice may be a liquid output measurement sensor in the connection pipe45. The sensor may also be a liquid output sensor in the delivery pipe41 or in the suction pipe 39 associated with the volumetric pump. Toachieve this it would also be possible to use a sensor for measuring thelevel of liquid inside the tank 7, associated with means for calculatingthe output of injected liquid from the variation in level of the tank 7as a function of time.

The second source of liquid is not necessarily a tank. The second sourcemay be a supply network of drinking water or industrial water, a well, acistern, or any other source containing a sufficient amount of water.The second source is preferably a source of pure water, but it couldalso be a source of any other type of liquid as long as this liquid,once sprayed on fruit and vegetables, does not cause problems.

The three-way valve inserted in the suction pipe of the volumetric pumpmay be replaced by two two-way valves, a two-way valve inserted in thesuction pipe of the volumetric pump and a two-way valve inserted in thesuction pipe connecting the second source of liquid to the suction pipe.

The means for supplying an emergency flow of liquid to the ejection pipemay alternatively comprise an emergency volumetric pump, the suctionarea of which is connected to the second source of liquid and thedelivery area of which is connected to the connection pipe.Alternatively, the emergency pump may be connected to a liquid inlet ofthe corresponding ejection pipe, which is distinct from the liquid inletconnected to the first source of liquid.

In the second embodiment of the invention, the injection pipe may not beconnected to a second liquid inlet of the ejection pipe, but rather tothe connection pipe. The injection of liquid from the second source isthus produced by the same liquid inlet as the injection of liquid comingfrom the first source.

In the second embodiment, the solenoid valve inserted in thepressurising pipe may be replaced by a solenoid valve inserted in theinjection pipe.

1. Device for the thermal fogging of a liquid, said device comprising: an unit for producing a stream of pressurised hot gas, having a hot gas outlet; an ejection pipe, having a hot gas inlet connected to the hot gas outlet of the production unit, and an ejection outlet for a mist of liquid; a first source of liquid; means for injecting a measured flow of liquid into the ejection pipe from the first source of liquid; wherein it comprises: a sensor for detecting a total or partial interruption of the measured flow of liquid injected into the ejection pipe from the first source of liquid; a second source of liquid; means for injecting an emergency flow of liquid into the ejection pipe from the second source of liquid when the sensor detects a total or partial interruption of the measured flow of liquid injected into the ejection pipe from the first source of liquid.
 2. Device according to claim 1, wherein the means for injecting a measured flow of liquid into the ejection pipe from the first source of liquid comprise a liquid measurement device, having a liquid suction inlet connected to the first source of liquid and a liquid delivery outlet connected to a liquid inlet of the ejection pipe, the means for injecting an emergency flow of liquid into the ejection pipe from the second source of liquid comprising a valve component suitable for selectively connecting the liquid suction inlet of the measurement device to the second source of liquid.
 3. Device according to claim 2, wherein the sensor is a temperature sensor suitable for measuring the current temperature of the gas in the ejection pipe downstream of the liquid inlet.
 4. Device according to claim 3, wherein it comprises a computer suitable for taking the current temperature of the gas measured by the sensor, comparing this current temperature with a predetermined maximum value, and actuating the valve component to connect the liquid suction inlet of the measurement device to the second source of liquid when the current temperature is higher than said predetermined maximum value.
 5. Device according to claim 3, wherein the valve component comprises a three-way valve comprising a first liquid inlet connected to the first source of liquid, a second liquid inlet connected to the second source of liquid and an outlet connected to the liquid suction inlet of the measurement device.
 6. Device according to claim 1, wherein the first source of liquid is a source of a liquid containing a chemical treatment agent, the second source of liquid being a source of a liquid that does not contain said chemical treatment agent.
 7. Device according to claim 1, wherein the second source of liquid is a source of water.
 8. Device according to claim 1, wherein the unit for producing a stream of pressurised hot gas comprises a fan, provided with a gas suction inlet and a pressurised gas delivery outlet, and a device for heating the gas under pressure, having a cold gas inlet connected to the delivery outlet of the fan, and an outlet forming the hot gas outlet.
 9. Device according to claim 8, wherein the second source of liquid is a substantially airtight tank, means for injecting an emergency flow of liquid into the ejection pipe from the second source of liquid comprising a pressurising pipe connecting the delivery outlet of the fan to a crown of the second source of liquid, and an injection pipe connecting the second source of liquid to a liquid inlet of the ejection pipe.
 10. Method for the thermal fogging of a liquid, said method comprising the following steps: creating a current of pressurised hot gas; injecting a flow of liquid into the pressurised hot gas from a first source of liquid; characterised by the following steps: detecting a total or partial interruption of the flow of liquid coming from the first source of liquid; injecting a flow of liquid into the heated pressurised gas from a second source of liquid when a total or partial interruption of the flow of liquid coming from the first source of liquid is detected. 